Oxidorhenium(v) complexes of a family of bipyridine-like ligands including pyridyltriazines and pyrazinyltriazine: Oxygen-atom transfer, metal redox and correlations

Article abstract of DOI:10.1002/ejic.200501102

The title ligands (general abbreviation L) are bipyridine (bpy), its dimethyl (mbpy) and diphenyl (pbpy) derivatives, phenanthroline (phen), 5,6-diphenyl-3-(2-pyridyl)-1,2,4-triazine (ppyt) and its dimethyl (mpyt) and pyrazinyl (ppzt) analogues. The concerned oxido complexes are [ReOCl ₃(L)], [ReOBr₃(ppyt)] and [ReOBr₃(ppzt)]. The chloro and bromo complexes of ppyt and ppzt were prepared by reacting these ligands with [ReOX₃(AsPh₃)₂] (X = Cl, Br). The X-ray structures of [ReOCl₃(ppyt)] and [ReOCl₃(ppzt)] reveal that the ReCl₃ fragment is meridionally disposed and that the L ligand is N,N-coordinated such that the pyridine/pyrazine nitrogen lies trans to the oxido oxygen atom. The Re-O lengths [1.656(10)/1.625(9) A] correspond to approximate triple bonding. The rate of oxygen-atom transfer from [ReOX₃(L)] to triphenylphosphane in solution follows second-order kinetics and is associated with a large and negative entropy of activation (approx. -30 cal K^-1 mol^-1). The initial attack is believed to involve the phosphane lone pair and Re≡O π*-orbitals. Electron withdrawal from the Re^VO moiety by varying X or L facilitates oxygen-atom transfer. Thus, the rates follow the orders Br < Cl; mbpy < bpy < phen < pbpy ? mpyt < ppyt < ppzt. The reduction potential of the quasireversible Re^VIO/Re^VO couple displays similar trends and the logarithmic rate constant of oxygen-atom transfer is found to correlate linearly with the reduction potential. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200501102

FULL PAPER
DOI: 10.1002/ejic.200501102
Oxidorhenium(
V
) Complexes of a Family of Bipyridine-Like Ligands Including
Pyridyltriazines and Pyrazinyltriazine: Oxygen-Atom Transfer, Metal Redox
and Correlations
Samir Das[a] and Animesh Chakravorty*[a,b]
Keywords: N ligands / Oxido ligands / Nitrogen heterocycles / Reduction potentials / Rhenium
The title ligands (general abbreviation L) are bipyridine
(bpy), its dimethyl (mbpy) and diphenyl (pbpy) derivatives,
phenanthroline (phen), 5,6-diphenyl-3-(2-pyridyl)-1,2,4-tri-
azine (ppyt) and its dimethyl (mpyt) and pyrazinyl (ppzt) ana-
logues. The concerned oxido complexes are [ReOCl3(L)],
[ReOBr3(ppyt)] and [ReOBr3(ppzt)]. The chloro and bromo
complexes of ppyt and ppzt were prepared by reacting these
ligands with [ReOX3(AsPh3)2] (X = Cl, Br). The X-ray struc-
tures of [ReOCl3(ppyt)] and [ReOCl3(ppzt)] reveal that the
ReCl3 fragment is meridionally disposed and that the L li-
gand is N,N-coordinated such that the pyridine/pyrazine ni-
trogen lies trans to the oxido oxygen atom. The Re–O lengths
[1.656(10)/1.625(9) Å] correspond to approximate triple
bonding. The rate of oxygen-atom transfer from [ReOX3(L)]
to triphenylphosphane in solution follows second-order ki-
netics and is associated with a large and negative entropy
of activation (approx. –30 calK–1 mol–1). The initial attack is
believed to involve the phosphane lone pair and ReϵO π*-
orbitals. Electron withdrawal from the ReVO moiety by vary-
ing X or L facilitates oxygen-atom transfer. Thus, the rates
follow the orders Br Ͻ Cl; mbpy Ͻ bpy Ͻ phen Ͻ pbpy ϽϽ
mpyt Ͻ ppyt Ͻ ppzt. The reduction potential of the quasire-
versible ReVIO/ReVO couple displays similar trends and the
logarithmic rate constant of oxygen-atom transfer is found to
correlate linearly with the reduction potential.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
The oxygen-atom transfer potency of the family of ReVO
complexes is estimated using triphenylphosphane as a
model oxophile. The systematics in the rate of oxygen-atom
transfer, which spans nearly two orders of magnitude, are
scrutinized in terms of electron withdrawal and metal re-
duction potential.
Introduction
The oxygen-atom transfer ability of the oxidorhenium()
moiety ReVO has been known for a long time,[1,2] and the
nature and scope of the process have attracted significant
recent attention.[3–9] In this laboratory we have been con-
cerned[10] with the design and reactivity of ReVO complexes
incorporating N,N-chelation by pyridyl ligands where the
second nitrogen site belongs either to an acyclic function,
such as an imine[11–13] or azo[13–16] group, or to a heterocy-
clic moiety. The scope of the latter alternative is potentially
wide because of the many interesting variations possible in
the form of aza-aromatic ligands.
Although a beginning in this direction was recently made
with pyridylazole ligands,[17,18] the logical starting point
would be the familiar didentate pyridyl aza-aromatic, viz.
bipyridine (bpy). This has prompted us to examine the
ReVO chemistry of bpy and certain bpy-like ligands includ-
ing pyridyltriazine and pyrazinyltriazine. Very little is cur-
rently known about rhenium binding by the latter two li-
gands (vide infra).
Results and Discussion
The ReVO Family
The ligand family used here consists of 1–4, each mem-
ber being abbreviated as shown below. The family spans
three distinct types of bpy modifications: simple substitu-
tion (as in 1), augmented conjugation (as in 2) and incorpo-
ration of nitrogen hetero atoms (as in 3 and 4).
The nine oxido complexes (Table 1) of 1–4 are of coordi-
nation type 5, abbreviated as [ReOX3(L)], where X = Cl or
Br.
The complexes of 1 and 2 (X = Cl) were conveniently
synthesised as yellow solids following a method previously
used for bpy.[19] The pink chelates [ReOCl3(L)] (L = 3 and
4) were prepared by the 1:1 reaction of [ReOCl3(AsPh3)2]
with L in benzene at room temperature. The use of the ar-
sane precursor is crucial for optimum yield. When [Re-
OCl3(PPh3)2] is employed the initially formed oxido com-
[a] Department of Inorganic Chemistry, Indian Association for the
Cultivation of Science,
Kolkata 700 032, India
Fax: +91-33-2473-2805
E-mail: icac@mahendra.iacs.res.in
[b] Jawaharlal Nehru Centre for Advanced Scientific Research,
Bangalore 560 064, India
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S. Das, A. Chakravorty
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an ReϵO stretch near 1000 cm–1 and two absorption bands
in the visible region around 500 and 750 nm, which are of
diagnostic value in rate studies (vide infra). The complexes
are diamagnetic (5d2) and show well-resolved 1H NMR
spectra, which have been assigned.
Of the complexes listed in Table 1, [ReOCl3(bpy)][19,21]
and [ReOCl3(phen)][22] have been reported before. The ana-
lytical[23] and coordination[24,25] chemistry of ppyt com-
plexes has been well-documented, but the only reported
rhenium complex is [Re(CO)3Cl(ppyt)],[26] which has re-
cently been structurally characterised in this laboratory.[20]
There is no report of rhenium complexes of mpyt and ppzt,
which have otherwise been only sparsely studied as li-
gands.[25,27]
Structure
The X-ray structures of [ReOCl3(ppyt)] (5e) and
[ReOCl3(ppzt)] (5h) were determined. Molecular views are
shown in Figures 1 and 2, respectively, and selected bond
parameters are listed in Table 2. In the distorted octahedral
ReOCl3N2 coordination sphere the chloride ligands are me-
ridionally disposed. In both molecules the coordinated ni-
trogen of the triazine ring is N2 and not N4, as also ob-
served in copper[24b] and ruthenium[27] chelates of ppyt/
ppzt. The coordinated pyridine nitrogen in 5e and pyrazine
nitrogen in 5h lie trans to the oxido ligand. In both cases
the chloride ligands and the triazine N2 atom define a good
equatorial plane (mean deviation: 0.03 Å) from which the
Re atom is displaced by 0.32 (5e) and 0.37 Å (5h) towards
the oxygen atom. The chelate ring in both cases is satisfac-
torily planar (mean deviation of about 0.06 Å). The two
heterocyclic rings deviate significantly from coplanarity, the
dihedral angles being 6.9° (5e) and 13.3° (5h).
Table 1. The type 5 oxido complexes, their ReVIO/ReVO reduction
potential (in Volt vs. SCE) and oxygen-atom transfer rate to PPh3.
Complex
E
[V] (∆Ep [mV])[a] 103k [–1 s–1][b,c]
½
[ReOCl3(bpy)] (5a)
[ReOCl3(mbpy)] (5b)
[ReOCl3(pbpy)] (5c)
[ReOCl3(phen)] (5d)
[ReOCl3(ppyt)] (5e)
[ReOBr3(ppyt)] (5f)
[ReOCl3(mpyt)] (5g)
[ReOCl3(ppzt)] (5h)
[ReOBr3(ppzt)] (5i)
1.45 (100)
1.44 (80)
1.48 (100)
1.47 (100)
1.61 (90)
1.58 (90)
1.53 (130)
1.68 (90)
1.65 (100)
1.60(0.03)
1.30(0.04)
2.52(0.04)
2.21(0.03)
25.01(0.02)
13.34(0.05)
10.45(0.05)
62.58(0.04)
36.64(0.06)
[a] In acetonitrile; ∆Ep is peak-to-peak separation. [b] In dichloro-
methane, temperature: 303 K. [c] Least-squares deviations are given
in parentheses.
plex reacts with the liberated phosphane (vide infra), which
affects the yield and purity of the product.
The use of [ReOBr3(AsPh3)2] in place of the chloro pre-
cursor gives the bromo system [ReOBr3(L)] for L = ppyt
and ppzt. Attempted synthesis of the iodo analogue from
[ReOI3(AsPh3)2] furnished only unstable products. How-
ever, in the presence of ArNH2 in the reaction mixture the
imido system [Re(NAr)I3(L)] could be isolated, which is a
possible intermediate in the formation of the ReVO ana-
logue.[20]
Figure 1. Molecular view and atom labelling scheme for [Re-
OCl3(ppyt)] (5e). All non-hydrogen atoms are represented by 30%
thermal probability ellipsoids. Hydrogen atoms have been omitted
Selected spectroscopic data for [ReOX3(L)] are collected
in the Experimental Section. The species uniformly display for clarity.
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Oxidorhenium() Complexes of a Family of Bipyridine-Like Ligands
FULL PAPER
a violet solution from which paramagnetic phosphane oxide
complexes of type [ReIII(OPPh3)X3(L)] have been isolated.
Characterisation data for two representative species are set
out in the Experimental Section. The observed room-tem-
perature magnetic moments (1.5–1.7 µB) are much lower
4
than the idealised spin-only value for the t2g configuration
due to strong orbital coupling, as is common for trivalent
1
rhenium. As expected, the H NMR spectra of the com-
plexes are paramagnetically shifted.[14,17,19,30]
Although no direct structural characterisation was pos-
sible due to lack of single crystals, our previous
work[11–18,31] on related systems strongly supports the gross
geometry of the phosphane oxide complexes to be 6.
The rate of the reaction of Equation (1) was determined
spectrophotometrically in dichloromethane solution.
Figure 2.Molecular view and atom labelling scheme for [Re-
OCl3(ppzt)] (5h). All non-hydrogen atoms are represented by 30%
thermal probability ellipsoids. Hydrogen atoms have been omitted
for clarity.
Table 2. Selected bond length [Å] and angles [°] for 5e and 5h.
5e
5h
Re–O
Re–N(1)
Re–N(2)
Re–Cl(1)
Re–Cl(2)
Re–Cl(3)
N(2)–N(3)
O–Re–N(2)
N(2)–Re–N(1)
N(2)–Re–Cl(1)
O–Re–Cl(2)
O–Re–Cl(3)
N(2)–Re–Cl(3)
Cl(1)–Re–Cl(3)
O–Re–N(1)
O–Re–Cl(1)
N(1)–Re–Cl(1)
N(2)–Re–Cl(2)
N(1)–Re–Cl(3)
Cl(2)–Re–Cl(3)
1.656(10)
2.262(11)
2.104(9)
2.313(4)
2.332(3)
2.363(3)
1.327(13)
90.5(4)
73.1(4)
164.4(3)
99.3(4)
97.8(4)
85.8(3)
88.77(14)
163.5(4)
104.8(4)
91.6(3)
91.4(3)
80.2(3)
1.625(9)
2.296(8)
2.124(7)
2.318(3)
2.345(3)
2.363(3)
1.330(10)
90.9(3)
Selected rate data are listed in Tables 1 and 3. A represen-
tative time-evolution spectrum characterised by isosbestic
points is shown in Figure 3. Under pseudo-first-order con-
71.9(3)
Table 3. Variable-temperature rate constants for the reaction [Re-
OCl3(L)] with PPh3 in dichloromethane solution.[a,b]
162.1(2)
100.3(3)
99.5(3)
T [K]
[PPh3] []
104kobs [s–1]
103k [–1 s–1]
87.4(2)
ppyt
293
0.012
0.015
0.019
0.012
0.015
0.019
0.012
0.015
0.019
0.012
0.015
0.019
0.012
0.015
0.019
0.012
0.015
0.019
0.012
0.015
0.019
0.012
0.015
0.019
1.452
1.814
2.300
2.000
2.509
3.177
3.001
3.750
4.752
3.935
4.920
6.232
4.300
5.375
6.808
5.958
7.448
9.434
7.510
9.388
11.891
10.501
13.126
16.627
12.08(0.05)
87.53(13)
162.9(3)
106.8(3)
90.3(2)
92.1(2)
79.9(2)
298
303
308
293
298
303
308
16.72(0.02)
25.01(0.02)
32.80(0.03)
35.38(0.09)
49.65(0.08)
62.58(0.04)
87.51(0.02)
162.76(14)
160.17(11)
The Re–O length, which corresponds to approximate tri-
ple bonding,[28] is somewhat longer in 5e [1.656(10) Å] than
in 5h [1.625(9) Å]. The Re–N1 bond lying trans to ReϵO is
longer than the Re–N2 bond by around 0.17 Å. Signifi-
cantly, the shorter Re–O bond in 5h is associated with a
longer Re–N1 bond. The structure of the bpy complex of
type 5, viz. [ReOBr3(bpy)], is known.[29] Here, the Re–O
distance is significantly longer [1.689(8) Å] than those in 5e
and 5h.
ppzt
Oxygen-Atom Transfer
[a] Initial concentrations of [ReOCl3(ppyt)] and [ReOCl3(ppzt)] are
5.43×10–5  and 4.65×10–5 , respectively. [b] Least-squares devi-
The [ReOX3(L)] (X = Cl, Br) complexes are uniformly
reactive towards triphenylphosphane in solution, furnishing ations are given in parentheses.
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S. Das, A. Chakravorty
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ditions (excess PPh3), the rate is proportional to the concen- twice as reactive as [ReOBr3(ppyt/ppzt)], in line with the
tration of the oxido complex, and the observed rate con- higher electronegativity of Cl. Again, the rate trend [Re-
stant, kobs, is proportional to the concentration of PPh3. OCl3(mbpy)] Ͻ [ReOCl3(bpy)] Ͻ [ReOCl3(pbpy)] correctly
The reaction is thus second order in nature, see Equa- reflects the electron-withdrawal power of the substituent
tion (2).
(Me Ͻ H Ͻ Ph). The [ReOCl3(phen)] complex fits between
the bpy and pbpy species. An increase in the number of
nitrogen hetero atoms is a very effective instrument for
achieving electron withdrawal.[32] Accordingly, the rate of
oxygen-atom transfer in the case of [ReOCl3(ppzt)] is 2.5
and 25 times faster than that for [ReOCl3(ppyt)] and [Re-
OCl3(pbpy)], respectively (Table 1).
While electron withdrawal from the ReVO moiety by li-
gand variation facilities oxygen-atom transfer, it is also ex-
pected to make metal oxidation more difficult. Fortunately,
the [ReOX3(L)] complexes are uniformly electroactive in
acetonitrile solution, exhibiting a quasi-reversible one-elec-
tron oxidative response near 1.5 V vs. SCE assigned to the
ReVIO/ReVO couple. Representative voltammograms are
shown in Figure 4 and reduction potential data are listed in
Table 1.
Figure 3. Time evolution spectra for the reaction of [ReOCl3(ppyt)]
and PPh3 in dichloromethane solution at 303 K (At is absorbance).
Rates for all the complexes were determined at 303 K
(Table 1), although in the cases of [ReOCl3(ppyt)] (5e) and
[ReOCl3(ppzt)] (5h) variable-temperature studies were also
made (Table 3). In both cases the rate constant, k, was
found to obey the Eyring equation. The activation param-
eters ∆H‡ and ∆S‡ are as follows: 11.66(0.26) kcalmol–1
and
–27.48(0.88) calK–1 mol–1
for
5e
and
9.94(0.28) kcalmol–1 and –31.95(0.95) calK–1 mol–1 for 5h.
The large and negative entropy of activation implies close
association of [ReOX3(L)] and PPh3 in the transition state,
as in the model 7,[10,17] where initial attack involves the
phosphane lone pair and ReϵO π*-orbitals.
Figure 4. Cyclic voltammograms of [ReOCl3(bpy)] (5a) and [Re-
OCl3(ppzt)] (5h) in acetonitrile solution at platinum working elec-
trode (scan rate: 100 mVs–1).
The data of Table 1 reveal that the rate of oxygen-atom
transfer rapidly increases with E of the ReVIO/ReVO cou-
½
ple. Indeed, there is a satisfactory linear correlation (corre-
lation constant 0.99) between the logarithmic rate constant
and the reduction potential (Figure 5). All the complexes
except 5g lie virtually on the least-squares line itself. The
Electron Withdrawal, Rate and Reduction Potential
The observed trend of reactivity is qualitatively consis- slope of the line is about 16. Evidently, a single linear equa-
tent with the reaction model. Electron withdrawal from the tion of this type cannot encompass all ReVO complexes but
ReVO moiety due to variation of X or due to modification it is gratifying to note that within a group where the L li-
of L is expected to favour the initial nucleophilic attack and gands belong to the same type (two six-membered N-het-
thereby facilitate oxygen-atom transfer. This is systemati- erocycles connected by a single bond) a simple correlation
cally observed. We note that [ReOCl3(ppyt/ppzt)] is nearly does exist.
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Oxidorhenium() Complexes of a Family of Bipyridine-Like Ligands
FULL PAPER
1
thermostatted cell compartments. H NMR spectra were recorded
with a Bruker FT 300 MHz spectrometer. The atom numbering
scheme used in 1H NMR is the same as in crystallography. Electro-
chemical measurements were performed under nitrogen with a CH
620A electrochemical analyzer, using a platinum working electrode.
The supporting electrolyte was tetraethylammonium perchlorate
(TEAP), and potentials are referred to the standard calomel elec-
trode (SCE). Room-temperature magnetic susceptibilities of pow-
ders were measured with a model 155 PAR vibrating sample mag-
netometer. Microanalyses (C,H,N) were performed using a Perkin–
Elmer 2400 series II elemental analyzer. Mass spectra were mea-
sured with Q-TOF mass spectrometer.
Synthesis of Complexes: The complex [ReOCl3(bpy)] (5a) was syn-
thesised from [ReOCl3(Me2S)(OPPh3)] and bpy by a reported pro-
cedure.[19] We found the procedure to be suitable for synthesis of
5b–5d as well with some modifications. Details are given below for
[ReOCl3(phen)] (5d).
[ReOCl3(phen)] (5d): A suspension of [ReOCl3(Me2S)(OPPh3)]
(84 mg, 0.13 mmol) and phen (30 mg, 0.15 mmol) in 10 mL of
tetrahydrofuran was stirred for 5 h. Filtration and washing with
diethyl ether (5×5 mL) gave 43 mg (0.09 mmol, 68%) of yellowish
5d in pure form. C12H8Cl3N2ORe (488.78): calcd. C 29.49, H 1.64,
N 5.73; found C 29.40, H 1.69, N 5.78. UV/Vis (CH2Cl2 solution:
λmax (ε) = 270 nm (56500 –1 cm–1), 410 (4150), 456 (5690), 795
Figure 5. Plot of logarithmic rate constant vs. ReVIO/ReVO re-
duction potential at 303 K.
Conclusion
In our search for reactive ReVO complexes of N,N-chelat-
ing heterocyclic ligands (L) the rhenium chemistry of the
pyridyl- and pyrazinyltriazine heterocycles ppyt, mpyt and
ppzt has been developed in the form of the complexes [Re-
OX3(L)] (X = Cl, Br), two of which have been structurally
characterised.
(160). IR (KBr): ν = 989 cm–1 (νReϵO). 1H NMR (300 MHz,
˜
CDCl3, 298 K): δ = 10.03 (d, J = 5.20 Hz, H1), 9.31 (d, J = 8.10 Hz,
H7), 8.98 (d, J = 5.01 Hz, H3), 8.62 (t, J = 7.62 Hz, H2), 8.60 (d,
J = 7.98 Hz, H9), 8.55 (d, J = 5.32 Hz, H12), 8.52 (d, J = 5.30 Hz,
H11), 8.30 (t, J = 8.02 Hz, H8) ppm.
[ReOCl3(mbpy)] (5b): Yield: 44 mg (69%.) C12H12Cl3N2ORe
These undergo strongly associative oxygen-atom transfer
to PPh3 (∆S‡ Ϸ –30 calK–1 mol–1). The rate of transfer has
also been determined for other [ReOCl3(L)] complexes (L
= bpy, mbpy, pbpy and phen). The oxygen-atom transfer
rates span nearly two orders of magnitude for the whole
family examined here.
Consistent with the proposed reaction model based on
nucleophilic attack of the PPh3 lone pair on π*(ReϵO) or-
bitals, the transfer rate increases systematically with increas-
ing electron withdrawal from ReVO due to variation of X
(Cl Ͼ Br) or L (ppzt Ͼ ppyt Ͼ mpyt ϾϾ pbpy Ͼ phen Ͼ
bpy Ͼ mbpy).
A second molecular parameter also responsive to elec-
tron withdrawal is the voltammetric ReVIO/ReVO reduction
potential, which shows the same trends as above. Indeed,
the logarithmic rate of transfer correlates linearly with the
ReVIO/ReVO reduction potential within the present family
of [ReOX3(L)] complexes.
(492.81): calcd. C 29.25, H 2.45, N 5.68 found C 29.30, H 2.40, N
5.60. UV/Vis (CH2Cl2 solution): λmax (ε) = 299 (47400), 458 (7670),
1
795 (225). IR (KBr): ν = 984 cm–1 (νReϵO). H NMR (300 MHz,
˜
[D6]DMSO, 298 K): δ = 8.92 (s, H4), 8.55 (s, H10), 8.40 (d, J =
5.85 Hz, H1), 8.10 (d, J = 6.06 Hz, H7), 7.48 (d, J = 6.03 Hz, H2),
7.40 (d, J = 5.79 Hz, H8), 4.70 (s, 3 H, 3-Me), 3.65 (s, 3 H, 9-Me)
ppm.
[ReOCl3(pbpy)] (5c): Yield: 52 mg (65%). C22H16Cl3N2ORe
(616.96): calcd. C 42.79, H 2.59, N 4.53; found C 42.70, H 2.53, N
4.58. UV/Vis (CH2Cl2 solution): λmax (ε)
=
326 nm
(50000 –1 cm–1), 465 (13100), 774 (253). IR (KBr): ν = 987 cm–1
˜
(νReϵO). 1H NMR (300 MHz, CDCl3, 298 K): δ = 9.08 (s, H4),
8.60 (d, J = 8.10 Hz, H1), 8.55 (d, J = 8.16 Hz, H2), 8.00–7.50 (m,
13 H, H3, H8, H10, 2Ph) ppm.
The Complexes 5e–5i: These complexes were prepared in 75–85%
yield by the same general procedure based on the reaction of [Re-
OX3(AsPh3)2] with L in benzene at room temperature. Details are
given here for a representative case.
[ReOCl3(ppyt)] (5e): The ligand ppyt (34 mg, 0.11 mmol) was added
to a suspension of [ReOCl3(AsPh3)2] (100 mg, 0.11 mmol) in 25 mL
of benzene. The resulting mixture was stirred for 1 h at room tem-
perature to produce a pink solution. The solvent was then removed
under reduced pressure. The solid mass thus obtained was repeat-
edly washed with n-hexane to remove the liberated AsPh3. The so-
lid was then dissolved in 5 mL of dichloromethane and subjected
to chromatography on a silica gel column (10×1 cm, 60–120 mesh)
prepared in toluene. The pink complex was eluted with pure dichlo-
romethane. Solvent removal from the eluate under reduced pressure
afforded [ReOCl3(ppyt)] in pure form, which was dried under vacuo
over fused calcium chloride. Yield: 53 mg (78%). C20H14Cl3N4ORe
(618.93): calcd. C 38.81, H 2.28, N 9.05; found C 38.87, H 2.21, N
Experimental Section
Materials: The complexes [ReOX3(AsPh3)2][33] and [ReOCl3(Me2S)-
(OPPh3)][19] and the triazine ligands[25,27] were prepared by reported
methods. The purification and drying of dichloromethane and ace-
tonitrile for spectral and electrochemical work was done as be-
fore.[34] Tetrahydrofuran and benzene ware dried using standard
methods. All other chemicals and solvent were of reagent grade
and were used as received.
Physical Measurements: UV/Vis spectral measurements were car-
ried out with a Shimadzu UVPC 1601 spectrometer fitted with
Eur. J. Inorg. Chem. 2006, 2285–2291
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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2289

S. Das, A. Chakravorty
FULL PAPER
9.09. UV/Vis (CH2Cl2 solution): λmax (ε)
=
306 nm
(CH2Cl2 solution): λmax (ε) = 289 nm (31300 –1 cm–1), 532 (8700),
1
(35400 –1 cm–1), 508 (13800), 736 (550). IR (KBr): ν = 1000 cm–1
701 (5150). IR (KBr): ν = 1119 cm–1 (νO=P). H NMR (300 MHz,
˜
˜
(νReϵO). 1H NMR (300 MHz, CDCl3, 298 K): δ = 8.91 (d, J = CDCl3, 298 K): δ = 25.99 (t, J = 9.00 Hz, H2), 10.19 (t, J =
9.09 Hz, H1), 8.52 (d, J = 7.41 Hz, H4), 8.14 (t, J = 7.20 Hz, H3),
7.50 Hz, H12), 9.58 (d, J = 8.40 Hz, 2 H, H16, H20), 9.50 (t, J =
7.94 (t, J = 7.74 Hz, H18), 7.72 (d, J = 7.98 Hz, 2 H, H10, H14), 7.50 Hz, 2 H, H11, H13), 8.22 (d, J = 7.80 Hz, H1), 8.10 (d, J =
7.64 (d, J = 7.05 Hz, 2 H, H16, H20), 7.59 (t, J = 7.95 Hz, 2 H,
H11, H13), 7.53 (t, J = 6.93 Hz, 2 H, H17, H19), 7.44 (t, J =
7.79 Hz, H12), 7.37 (t, J = 6.60 Hz, H2) ppm.
8.10 Hz, 2 H, H10, H14), 7.73 (t, J = 7.20 Hz, H18), 7.17 [d, J =
7.20 Hz, 6 H, o-H(PPh3)], 6.77 [t, J = 7.50 Hz, 3 H, p-H(PPh3)],
5.06 (t, J = 7.50 Hz, 2 H, H17, H19), 4.00 [t, J = 7.80 Hz, 6 H, m-
H(PPh3)], 2.79 (d, J = 4.80 Hz, H4), –17.01 (t, J = 9.00 Hz, H3)
[ReOBr3(ppyt)] (5f): Yield: 60 mg (80%). C20H14Br3N4ORe
(752.28): calcd. C 31.93, H 1.88, N 7.45; found C 31.90, H 1.93, N
ppm. E (ReIV/ReIII couple): 0.33 V (∆Ep = 70 mV). µ (in powder):
½
1.51 µB (298 K). Q-TOF-MS: m/z 881.30.
7.40. UV/Vis (CH2Cl2 solution): λmax (ε)
=
302 nm
(34300 –1 cm–1), 514 (10900), 726 (1050). IR (KBr): ν = 996 cm–1
[Re(OPPh3)Br3(ppzt)]: Yield: 104 mg (79%). C37H28Br3N5OPRe
˜
(νReϵO). 1H NMR (300 MHz, CDCl3, 298 K): δ = 8.92 (d, J =
5.82 Hz, H1), 8.51 (d, J = 7.89 Hz, H4), 8.14 (t, J = 7.77 Hz, H3),
7.72 (d, J = 7.41 Hz, 2 H, H10, H14), 7.63 (d, J = 7.08 Hz, 2 H,
H16, H20), 7.58 (t, J = 8.88 Hz, 2 H, H11, H13), 7.53 (t, J =
8.22 Hz, 2 H, H17, H19), 7.42 (t, J = 7.68 Hz, H12), 7.42 (t, J =
7.74 Hz, H18), 7.34 (t, J = 5.24 Hz, H2) ppm.
(1015.56): calcd. C 43.76, H 2.78, N 6.96; found C 43.70, H 2.73,
N
6.83. UV/Vis (CH2Cl2 solution): λmax (ε)
=
300 nm
(32900 –1 cm–1), 525 (8400), 665 (5900). IR (KBr): ν = 1121 cm–1
˜
(νO=P). 1H NMR (300 MHz, CDCl3, 298 K): δ = 42.83 (d, J =
7.11 Hz, H1), 21.98 (s, H3), 8.78 (t, J = 7.62 Hz, 2 H, H10, H12),
8.62 (d, J = 7.08 Hz, 2 H, H9, H13), 7.93 (t, J = 6.87 Hz, H11),
7.68 (d, J = 7.89 Hz, H2), 7.41 [d, J = 6.72 Hz, 6 H, o-H(PPh3)],
6.96 [t, J = 6.96 Hz, 3 H, p-H (PPh3)], 6.27 (t, J = 6.36 Hz, H17),
6.13 [t, J = 8.03 Hz, 6 H, m-H(PPh3)], 5.67 (t, J = 7.44 Hz, 2 H,
[ReOCl3(mpyt)] (5g): Yield: 41 mg (75%). C10H10Cl3N4ORe
(494.79): calcd. C 24.27, H 2.04, N 11.32; found C 24.30, H 2.08,
N
11.40. UV/Vis (CH2Cl2 solution): λmax (ε) = 300 nm
H16, H18), 4.61 (d, J = 7.74 Hz, 2 H, H15, H19) ppm. E (ReIV
/
½
(32900 –1 cm–1), 496 (6800), 701 (950). IR (KBr): ν = 994 cm–1
˜
ReIII couple): 0.58 V (∆Ep = 90 mV). µ (in powder): 1.67 µB
(νReϵO). 1H NMR (300 MHz, CDCl3, 298 K): δ = 8.74 (d, J =
5.02 Hz, H1), 7.92 (t, J = 7.77 Hz, H3), 7.76 (d, J = 7.74 Hz, H4),
7.60 (t, J = 5.90 Hz, H2), 2.68 (s, 3 H, 7-Me), 2.64 (s, 3 H, 8-Me)
ppm.
(298 K). Q-TOF-MS: m/z 1015.34.
Rate Measurement: The representative case of the reaction of [Re-
OCl3(ppyt)] with PPh3 will be described. A known excess of PPh3
was added to a solution of [ReOCl3(ppyt)] (5.43×10–5 ) in dichlo-
romethane at the desired temperature, and the thermostatted reac-
tion was followed spectrophotometrically (quartz cell; path length:
1 cm) by measuring the absorbance (Aα) of the peak at 710 nm as
a function of time (t). The absorbance (Aα) at the end of the reac-
tion (24 h) was also measured. Values of kobs and k were obtained
from the slopes of the linear plots of –[ln(Aα – At)] vs. t and kobs
vs. [PPh3] respectively. The activation enthalpy and entropy param-
eters were determined from the linear plot of –ln(kh/kBT) vs. T–1
using the Eyring equation, see Equation (3).
[ReOCl3(ppzt)] (5h): Yield: 57 mg (83%). C19H13Cl3N5ORe
(619.92): calcd. C 36.81, H 2.11, N 11.30; found C 36.86, H 2.17,
N
11.35. UV/Vis (CH2Cl2 solution): λmax (ε) = 310 nm
(36400 –1 cm–1), 523 (13800), 737 (540). IR (KBr): ν = 1004 cm–1
˜
(νReϵO). 1H NMR (300 MHz, CDCl3, 298 K): δ = 9.95 (s, H3),
8.85 (d, J = 6.00 Hz, H2), 7.95 (d, J = 4.20 Hz, 2 H, H9, H13),
7.88 (d, J = 7.20 Hz, H1), 7.74 (d, J = 7.80 Hz, 2 H, H15, H19),
7.65 (t, J = 6.90 Hz, 2 H, H10, H12), 7.54 (t, J = 10.80 Hz, 2 H,
H16, H18), 7.45 (t, J = 7.80 Hz, H11), 7.45 (t, J = 7.80 Hz, H17)
ppm.
[ReOBr3(ppzt)] (5i): Yield: 64 mg (85%). C19H13Br3N5ORe
(753.27): calcd. C 30.30, H 1.74, N 9.30; found C 30.25, H 1.70, N
9.24. UV/Vis (CH2Cl2 solution): λmax (ε)
=
310 nm
(35100 –1 cm–1), 531 (10600), 739 (850). IR (KBr): ν = 999 cm–1
˜
Crystal Structure Determination: Single crystals of the complexes
[ReOCl3(ppyt)] (5e) and [ReOCl3(ppzt)] (5h) were grown by slow
diffusion of hexane into dichloromethane solutions of the respec-
tive compounds. Data were collected on a Nicolet R3m/V four-
circle diffractometer with graphite-monochromated Mo-Kα radia-
tion (λ = 0.71073 Å) by the ω-scan technique in the range 3° Յ 2θ
Ͻ 50°. All data were corrected for Lorentz-polarisation and ab-
sorption.[35] The metal atoms were located from Patterson maps
and the rest of the non-hydrogen atoms emerged from successive
Fourier syntheses. The structures were then refined by a full-matrix
least-squares procedure on F2. All non-hydrogen atoms were re-
fined anisotropically. All hydrogen atoms were included in calcu-
lated positions. Calculations were performed using the
SHELXTLTM V 5.03 program package.[36]
(νReϵO). 1H NMR (300 MHz, CDCl3, 298 K): δ = 9.75 (s, H3),
8.81 (d, J = 4.76 Hz, H2), 8.60 (d, J = 4.88 Hz, H1), 7.74 (d, J =
7.59 Hz, 2 H, H9, H13), 7.66 (d, J = 6.42 Hz, 2 H, H15, H19), 7.56
(t, J = 7.80 Hz, 2 H, H10, H12), 7.52 (t, J = 6.42 Hz, 2 H, H16,
H18), 7.48 (t, J = 5.90 Hz, H11), 7.46 (t, J = 7.44 Hz, H17) ppm.
Complexes [Re(OPPh3)Cl3(L)]: These were prepared in 75–80%
yield by the same general procedure based on the reaction of [Re-
OX3(L)] with triphenylphosphane in benzene at room temperature.
Details are given below for a representative case and data for a
second compound prepared analogously follow.
[Re(OPPh3)Cl3(ppyt)]: PPh3 (68 mg, 0.28 mmol) was added to a
solution of [ReOCl3(ppyt)] (80 mg, 0.13 mmol) in 25 mL of dichlo-
romethane. The resulting solution was magnetically stirred for 4 h
at room temperature and during this time the colour of the solution
changed from pink to violet. It was then subjected to chromatog-
raphy on a silica gel column. Excess PPh3 was eluted with benzene.
A violet band was eluted with a benzene/acetonitrile (25:2) mixture.
The solvent was removed under reduced pressure and the violet
complex so obtained was dried under vacuo over fused calcium
Data for 5e: C20H14Cl3N4ORe, monoclinic, P21/n, a = 8.920(2), b
= 15.021(3), c = 15.558(3) Å, β = 92.05(3)°, V = 2083.2(3) Å3, Z =
4, 3111 unique reflections (Rint = 0.0000). Final residuals R1
0.0556 and wR2 = 0.1405 [I Ͼ 2σ(I)].
=
Data for 5h: C19H13Cl3N5ORe, monoclinic, P21/c, a = 9.274(2), b
= 16.418(3), c = 13.732(3) Å, β = 98.70(3)°, V = 2066.8(7) Å3, Z =
chloride. Yield: 90 mg (75%). C38H29Cl3N4OPRe (881.22): calcd. 4, 3617 unique reflections (Rint = 0.0648). Final residuals R1
C 51.80, H 3.32, N 6.35; found C 51.72, H 3.39, N 6.30. UV/Vis 0.0472 and wR2 = 0.1154 [I Ͼ 2σ(I)].
=
2290
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Eur. J. Inorg. Chem. 2006, 2285–2291

Oxidorhenium() Complexes of a Family of Bipyridine-Like Ligands
FULL PAPER
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CCDC-292211 and -292212 contain the supplementary crystallo-
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Received: December 8, 2005
Published Online: April 4, 2006
Eur. J. Inorg. Chem. 2006, 2285–2291
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2291